Mestastic colorectal cancer (CRC) is the third leading cause of cancer deaths among men and women in the US. Untreated metastic CRC only has a 8% 5 year survival, while treatment increases this survival rate to 30-35% (American Cancer Society Statistics 2004). However, only 20% of patients with CRC liver metastases are suitable for resection. This motivates the development of curative non-invasive treatment option. In this project, we will develop a high intensity focused ultrasound (HIFU) probe for treatment of malignancies in the upper abdomen organs. Though piezoelectric transducers have been traditionally used for therapeutic probes, this technology often suffers from difficulty in fabrication, reliability, and overheating. We propose using capacitive micromachined ultrasonic transducers (CMUTs) for HIFU. Not only are CMUTs easily fabricated using standard silicon processing techniques, which provide a cost-effective alternative, they also offer advantages like fabrication flexibility and direct integration with electronics. These advantages enable more flexible and reconfigurable therapeutic arrays for complex beamforming through layers of tissue. Furthermore, since CMUTs are not resonance structures, they have excellent bandwidth and efficiency. While imaging CMUTs have demonstrated excellent performance, a CMUT designed specifically for HIFU has not yet been designed. This project seeks to design and develop a prototype CMUT HIFU probe designed for MR-guided thermal therapy of liver and renal cancer. More specifically, we aim to: (1) Design and fabricate test CMUTs transducers specifically for HIFU; these test transducers will allow us to modify our designs and refine our finite element models to improve transducer performance and reliability. (2) Design, fabricate, and package an annular ring CMUT HIFU probe and electronics system for use in the MR scanner; the beam profile and reliability of this probe will be measured and refined as needed. (3) Fabricate a final CMUT probe packaged for use within a MR scanner. This probe will be integrated in the MR-guidance system and compared to conventional piezoelectric devices. Upon completion, the project will have developed a CMUT HIFU probe capable for MR-guided treatment of cancer that will be ready for in vivo testing. The success of this project will greatly increase the treatment options for the 80% of CRC and upper abdomenal cancer patients who are not suitable for resection, thereby reducing morbidity and mortality. [unreadable] [unreadable] [unreadable]